(adapted from Merriam-Webster online, www.m-w.com)
hydrogen: The simplest and lightest of the elements, it is normally a colorless odorless highly flammable gas.
infrared light: Light made of waves that are too long for human beings to see with their eyes.
fusion: The joining together of atomic nuclei to form heavier nuclei, resulting in the release of enormous quantities of energy.
helium: A light colorless inert gaseous element found especially in natural gases. In the core of most stars, helium is formed when hydrogen atoms join together in fusion.